I've had HG with each pregnancy and ended up on a zofran pump last time. You need to really UP your water intake with the zofran. The oral med actually loses effectiveness the less hydrated you are, which is why I ended up on the pump. Upping water intake and adding a fiber supplement like Benefiber (to any non-carbonated drink) took care of 90% of any intestinal issues I had.
If you are unsure if you're getting enough water, grab some ketone strips from the pharmacy (in the diabetic care section). If you test positive for ketones, you have some level of dehydration going and need to up fluids more.